Ethanol at concentrations greater than or qual too 0.08 g/dl significantly impairs motor skills and this effect is responsible for the majority of traffic accident-related deaths in the United States. Importantly, individuals with low sensitivity to this action of ethanol are more likely to develop alcoholism. In addition, chronic alcoholism and fetal alcohol syndrome are associated with significant decreases in the number of cerebellar neurons. Therefore, understanding the mechanism of action of ethanol in the cerebellum is an area of tremendous interest. Neurons of the cerebellar cortex play a central role in the control of motor functions. These neurons form a basic circuit unit and Purkinje neurons are the main output of this circuit. Purkinje neurons receive excitatory inputs from the spinal cord and brain stem via mossy fibers and from the inferior olive via climbing fibers. These neurons also receive inhibitory input from molecular layer interneurons. Excitatory input from the mossy fibers is relayed to Purkinje neurons by the cerebellar granule cells and these cells are under the inhibitory control of Golgi interneurons. Preliminary data indicate that acute ethanol exposure increases GABAergic tone at Golgi interneuron-to-granule cell synapses and at molecular layer interneuron-to-Purkinje neuron synapses. Moreover, it also inhibits excitatory input at climbing fiber-to-Purkinje neuron synapses. We hypothesize that ethanol depresses synaptic transmission in the mature cerebellar cortex by presynaptically modulating neurotransmitter release at major synapses within the basic circuit unit. We propose to use the acute cerebellar slice preparation and patch-clamp electrophysiological techniques to test this hypothesis. Specific Aim #1 is to investigate the acute effect of ethanol on neurons of the granule cell layer. We will assess the effect of ethanol on GABAergic transmission at granule cells and its impact on the excitability of these cells. We will also evaluate the effects of ethanol on Golgi cell excitability. Specific Aim #2 is to investigate the acute effects of ethanol on neurons of the Purkinje and molecular layers. We will measure the effects of ethanol on Purkinje cell firing in response to stimulation of the mossy fiber granule cell pathway or the parallel fiber pathway. We will assess the effect of ethanol on the frequency of mIPSCs evoked by action potential-independent GABA release at molecular layer interneuron-to-Purkinje cell synapses. Finally, we will evaluate the mechanism by which ethanol affects the complex spike evoked in Purkinje cells by stimulation of climbing fibers. Together, these experiments will provide a comprehensive view of the acute effects of ethanol on mature cerebellar synapses of the cerebellar cortex. This type of comprehensive study has not been performed before and it will significantly increase our understanding of the mechanism of action of ethanol in the central nervous system.